Blast-exposure or non-blast-related traumatic brain injury (TBI), resulting from incidents such as falls, sports concussion, or motor vehicle accidents, are prevalent injuries sustained by Operation Enduring Freedom and Operation Iraqi Freedom Veterans. Individuals with a history of these brain injuries often report substantial difficulties understanding speech in noise despite having normal peripheral hearing sensitivity. Research has shown that Veterans with a history of exposure to high-intensity blasts show deficits on neural and behavioral measures that reflect auditory processing at the level of the cortex, while measures that reflect the integrity of subcortical auditory processing mechanisms appear to be unaffected. However, recent research on civilians with non-blast TBI suggest that this type of brain injury impacts neural processing mechanisms that are different than those impacted by blast exposure. For instance, unlike results from individuals with a history of blast exposure, several research studies have shown that civilians with non-blast TBI do show deficits on neural and behavioral measures that rely on the integrity of auditory processing in subcortical structures, such as the brainstem and midbrain. The long-term goal of our research program is to develop effective assessment and individualized auditory rehabilitation methods for individuals with brain injury who have substantial difficulties communicating in noise. Our specific objectives for this CDA-1 proposal are to identify the effects of non-blast TBI on subcortical and cortical auditory processing using a comprehensive battery of electrophysiological and behavioral measures and to identify measures that are predictive of speech understanding in noise deficits in individuals with non-blast TBI. Specifically, we will 1) identify patterns of subcortical and cortical processing deficits from a battery of electrophysiological and behavioral measures previously collected from Veterans with a history of non-blast TBI and control Veteran participants with no history of blast or TBI, and 2) determine relationships between responses from electrophysiological and behavioral auditory processing measures and measures of speech perception in noise in a new, larger group of Veterans and civilians with non-blast TBI. For our first aim, we will perform exploratory analyses on an existing data set of neural and behavioral measures to identify particular test measures that show effects of non-blast TBI on auditory processing and which should be prioritized for further testing on a new, larger group of participants with non-blast TBI. For our second aim, we will collect data from this new, larger sample of participants with non-blast TBI on measures identified in Aim 1 as well as additional, new measures identified from the literature, to identify potential subcortical and cortical processing measures that are predictive of impaired speech understanding in noise. We hypothesize that analysis in Aim 1 will reveal that several neural and behavioral measures which rely on the integrity of subcortical and cortical processing mechanisms will reveal significant effects of non-blast TBI which should be prioritized for testing in Aim 2. In addition, we hypothesis that a combination of measures that reflect subcortical and cortical processing abilities will be most predictive of measured and self-reported difficulties understanding speech in noise. The expected outcomes of this research proposal include a better understanding of effects of non-blast TBI on measures of subcortical and cortical processing that impact the perception of speech in noise. These results will have a significant positive impact by identifying test measures and analysis techniques that should be used in future studies that examine the effects of brain injury on communication difficulties, which will provide strong evidence for processing mechanisms that should be specifically targeted in the future development of clinical auditory assessment and rehabilitation methods for civilians and Veterans with brain injury.